Water Spider From 520 Million Years Ago Solves Puzzle

Oct. 16 (Bloomberg) -- The fossil of an extinct marine
spider, discovered in China 520 million years after it lived in
the ocean, has helped scientists solve an ancestral puzzle on
where the anthropod fits on the evolutionary map.

Using comparisons of central nervous systems, scientists
were able to prove that megacheirans, the name given to the
extinct group, are related to chelicerates, which include
spiders and scorpions, according to a study in the journal
Nature today. The findings also show that the 3-centimeter-long
(1.2-inch-long) spider’s ancestors branched off from the family
tree of other arthropods, which include insects, crabs and
millipedes, more than half a billion years ago.

“For the first time we can analyze how the segments of
these fossil arthropods line up with each other the same way as
we do with living species,” said Greg Edgecombe, a researcher
of invertebrates and plants at London’s Natural History Museum
and a co-author of the study.

An analysis of the fossilized creature’s nervous system
showed similarities to today’s horseshoe crabs and scorpions,
suggesting it once dwelled among ancestors of crustaceans,
Nicholas Strausfeld, a professor in the University of Arizona’s
department of neuroscience and senior author of the study, said
in a statement. It had an elongated body with a dozen pairs of
appendages that helped it to swim, as well as a scissor-like
appendage on its head that was probably used to sense its
environment or to grasp, researchers said.

The team analyzed the fossil by applying different imaging
techniques, taking advantage of iron deposits that had
accumulated in the nervous system during fossilization. The
remains are of the earliest known complete nervous system,
according to the release that accompanied the report.